1. Field of the Invention
The present invention relates to a communication system for wireless data transmission/reception and to a wireless communication equipment used in such a system. More specifically, the present invention relates to a communication system and wireless communication equipments which allow automatic switching between direct transmission and relayed transmission in which data is transmitted from a transmission source equipment to a transmission destination equipment through a relay.
2. Description of the Background Art
Recently, much effort has been made to substitute wireless medium such as radio wave, infrared wave or ultrasonic wave for wired medium such as a coaxial cable or a twisted pair as the communication medium, in order to facilitate moving and layout of electronic equipments such as personal computers connected to LAN (Local Area Network). At present, wireless LAN products such as boards for personal computers have come to be commercially available.
Further, as portable terminals such as a so called electronic organizer have been improved to have wider variety of functions, portable terminals having communication function have been produced. At present, one to one communication is dominant in the field of wireless communication between portable terminals. However, N to N communication employing a wireless network including three or more portable terminals has been developed.
Data transmitted/received between the terminals are transmitted in the form of packets. FIG. 1 shows configuration of a packet 30 used in a conventional communication system. When wireless communication takes place between three or more communication equipments, the packet transmitted by the transmission source equipment is received not only by the transmission destination equipment but also by other communication equipments. Therefore, it is necessary to make clear from which communication equipment to which communication equipment the data is transmitted. For this purpose, packet 30 includes, in addition to the transmission data 38, an identification code 34 indicating transmission source equipment of the data, and an identification code 36 indicative of the transmission destination equipment of the data. Packet 30 further includes a packet type code 32 indicating the type of the packet, and other information 40. The communication equipment which has received the packet determines, depending on whether the data transmission destination identification code of the received packet matches the identification code of itself, whether the data is destined to it. The communication equipment which has received the data destined to it transmits a reception response packet to the transmission source equipment, so as to notify that the data has been received.
A conventional wireless communication system allows communication where direct communication between each of the equipment is possible. The conventional technique does not allow direct wireless communication between equipments between which wireless signals do not directly reach. In order to cope with this problem, the conventional wireless communication system further includes a wired network having a plurality of access points. In such a system, wireless communication is established between a terminal and an access point, and wired communication is established between each of the access points. Such a communication network presumes and is suitable for an environment in which terminals are stationary or terminals move only within a small range. Therefore, communication between terminals in the network is always possible after the operation of the network is confirmed when the terminals are set. Accordingly, arrangement of wire medium can be minimized.
However, there arises a new problem when terminals moving in a wide range such as portable terminals are to be used. More specifically, the portable terminal moves with the user, and hence the distance between the terminal and an access point vary widely. A condition where wireless communication between the terminal and the access point becomes impossible is more likely. Wireless direct communication between portable terminals without using a wire medium is possible. However, it is highly likely that the communication between portable terminals which has been successful so far suddenly becomes impossible if position of a terminal with respect to another terminal changes.
Routing technique used in the Internet has been known as a technique for establishing communication between terminals incapable of direct communication, through other equipments. However, the routing technique, which was originally developed for a wired network, cannot be applied as it is to a wireless network where state of connection with each terminal to the network may vary. Further, the routing technique requires its relaying equipment of high performance. Therefore, structures of the equipments constituting the network cannot be simplified.
The packet configuration shown in FIG. 1 may be utilized when relayed transmission is to be performed with a relay equipment determined in advance. However, as a relay equipment is fixed, the conventional packet configuration is not suitable for wireless communication network constituted by portable terminals in which condition allowing direct transmission tends to change considerably. When direct transmission from a transmission source equipment to a transmission destination equipment is not possible and relayed transmission through a relay equipment is desired, relayed transmission is not possible either, if direct transmission from the transmission source equipment to the relay equipment or direct transmission from the relay equipment to the transmission destination equipment is impossible.